This invention relates to accelerometers.
The invention is more particularly concerned with accelerometers for providing an optical output.
It is an object of the present invention to provide an accelerometer that can provide an optical output which is independent of the effects of temperature change.
According to the present invention there is provided an accelerometer including first and second compliant members having respective axes arranged parallel with one another, a support that supports the compliant members at a first end, a first mass mounted at the second end of the first compliant member, a second mass identical with the first mass mounted at the second end of the second compliant member opposite the first mass, first and second optical fibers exhibiting birefringence wound around respective ones of the compliant members such that acceleration axially of the compliant members compresses one of the compliant members and extends the other compliant member so as to produce equal and opposite changes in birefringence in the first and second optical fibers, and means responsive to the change in birefringence of both fibers that is arranged to produce an output representative of acceleration which is independent of temperature.
The first and second compliant members are preferably arranged axially of one another with the first end of the compliant members adjacent one another. The first and second compliant members are preferably provided by opposite ends of a compliant cylinder supported midway along its length. The cylinder may be of circular section. The compliant members may be of an elastomeric material. The first and second optical fibers preferably both have a core of elliptical section, the major axis of the elliptical section of each fiber extending parallel to the axis of the compliant members.
The accelerometer may include a source of radiation that is arranged to supply radiation to one end of both optical fibers, a first detector arranged to receive radiation from the opposite end of the first optical fiber and, a second detector arranged to receive radiation from the opposite end of the second optical fiber. The accelerometer may include a first polarizer located between the opposite end of the first optical fiber and the first detector, and a second polarizer located between the opposite end of the second optical fiber and the second detector, the first and second polarizers being arranged such that a maximum level of radiation is incident on the detectors for a minimum applied acceleration. The accelerometer preferably includes processor means connected with the first and second detectors, the processor means being arranged to determine for each fiber, the change in values of birefringence cause by applied acceleration and to subtract these values from one another.
An accelerometer according to the present invention will now be described, by way of example, with reference to the accompanying drawings.